تقييم خاصية التشقق لمزيج البيتومين المستحلب البارد

Evaluating the Fracture Characteristic of Cold Bitumen Emulsion Mixtures

Abstract

Fracture is a primary cause of asphalt pavement distresses, making the evaluation of fracture properties crucial for improved pavement design. cold bitumen emulsion mixtures (CBEMs) offer a sustainable alternative but are suffered from high air voids, moisture presence, slow curing, and low early strength. While modifications using cementitious materials enhance early strength, they often lead to increased brittleness and poor fracture resistance. Thus, advancing CBEMs with balanced early strength and improved cracking resistance is essential, especially given the limited research in this area. This study developed a CBEM for binder course applications using a ternary-blended cementitious filler (TBF) composed of metakaolin (MK), palm leaf ash (PLA), and ordinary Portland cement (OPC) as a replacement for traditional limestone filler (LF), and reinforced with micro-fibers (glass fiber (GF), polypropylene (PP)) and macro-fibers (polyethylene terephthalate (PET)). A superplasticizer (SP) was added to reduce air voids and improve early strength by lowering water content. Laboratory testing, including volumetric and indirect tensile strength (ITS) tests, was conducted to determine optimal proportions, with strength evaluated at 3, 7, 14, and 28 days. Fracture properties were characterized using ITS, semi-circular bending (SCB), and four-point bending (4PB) tests, supported by image analysis under ageing and moisture conditions.
Fracture performance was assessed through ITS using indices such as fracture energy (Gf), cracking tolerance index (CT-Index), Illinois flexibility index (FI), crack resistance index (CRI), normalized flexibility factor (Nflex), toughness index (TI), and fracture strain tolerance (FST) index. SCB tests, supported by digital image analysis (which captured crack initiation, propagation length, and crack mouth opening displacement (CMOD)), provided Gf, critical energy release (Jc), resistance curve (R-curve), and strain maps for crack behavior evaluation. The 4PB test further provided Gf, maximum load-displacement, and deflection before failure. The results revealed that the TBFSP-FG+PET-CBEM mixture, incorporating TBF as a replacement for LF, reinforced with micro-GF and macro-PET fibers, and enhanced with SP, significantly outperformed the control C-CBEM mixture. After 3 days of curing, it achieved 4.4 times higher strength. It also showed superior cracking resistance at both early and later ages, with fracture energy increasing by 5.8 times at 3 days and 9.2 times at 28 days compared to C-CBEM, and 7.4% higher than HMA at 28 days. ITS cracking indices (CT-index) reached 78 and 170 after 3 and 28 days, respectively, 2.4 and 21 times higher than C-CBEM. SCB test results showed a substantial increase in Jc and a distinct R-curve pattern, with 21 times and 3.14 times more fracture energy at crack initiation than C-CBEM and HMA, respectively. The 4PB test confirmed higher maximum load, Gf, displacement, and deflection before failure. These findings align with ITS and SCB test results. The mixture also exhibited satisfactory resistance results to ageing and moisture. Digital image analysis revealed enhanced plastic deformation due to micro-GF and macro-PET fibers. This study offers valuable insights into advancing CBEM as sustainable alternatives to traditional HMA, while enhancing understanding of their fracture behavior for more durable and flexible pavements.